In an indoor environment that has a complicated structure and bottleneck portions, such as a reactor building in a nuclear power plant, tasks of transporting long and heavy objects such as pipes, shields, and protection sheets for maintenance works are carried out by workers. In a high-radiation area, however, workers are not allowed to work for a long period of time. Therefore, realization of operations by remote-controlled robots is expected.
As a coordinated transport operation to be performed by robots, there is a first example in which an industrial vertical articulated robot arm is mounted on a movable carriage, and the reaction forces mutually acting on the robots are absorbed by performing force control. In the first example, if the transport object is a rigid object, the spaces between the robots are restricted to some degree, and accordingly, the errors in the distances between the robots can be absorbed in the movement range of the arm. Meanwhile, a second example related to coordinated transport is also known.
As the articulated robot arm used in the first example has multiple degrees of freedom, the articulated robot arm can absorb not only position errors but also posture errors. However, the load on the system, such as the weight and power consumption, becomes large. Furthermore, the responsiveness to control is normally not high. Meanwhile, a mechanism formed only with passive elements is simple and is light in weight, but does not have a very high tolerance to posture errors.
The second example discloses a coordinated transport method involving more than one mobile robot. However, the mobile robots are limited to those of an independent-two-wheel type, and furthermore, an internal force generated by a transport object is measured with a force sensor. Since a force sensor breaks down when subjected to a large moment such as impact, the transport method according to the second example is not suitable for transporting heavy objects.